Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1995-10-25
2001-05-22
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S043000, C358S296000
Reexamination Certificate
active
06234600
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image recording apparatus.
2. Description of the Related Art
An ink jet recording apparatus which performs printing (recording) by discharging ink onto a recording medium is known as one of the conventional image recording apparatuses.
Ink jet recording apparatus have been rapidly spread recently because they are non-impact type recording apparatus and producing little noise, and color image recording can be easily implemented by using multiple inks.
FIG. 1
is a schematic perspective view showing a conventional ink jet recording apparatus.
In
FIG. 1
, a recording medium
5
wound in a roll passes transport rollers
1
and
2
, is held by paper incrementing rollers
3
, and is incremented in the direction of f in
FIG. 1
by the driving of a subscanning motor
4
coupled to one of the incrementing roller
3
. Across the recording medium
5
, guide rails
6
and
7
are disposed in parallel, and a carriage
8
is mounted thereon. The carriage
8
moves in the lateral direction so that a recording head unit
9
mounted thereon is scanned in that direction. On the carriage
8
, four color recording heads
9
Y,
9
M,
9
C and
9
Bk for yellow, magenta, cyan and black are mounted, and four ink reservoirs corresponding to those colors are disposed. Each head includes a orifice array including a plurality of ink orifices, and orifice arrays of the heads are disposed in parallel. The recording medium
5
is intermittently incremented by the amount of recording of the head unit
9
, and the head unit
9
is scanned in the direction P discharging ink droplets in accordance with a binary image signal while the recording medium is stationary.
With such an ink jet recording apparatus, the recording medium characteristics are very important. In particular, ink running characteristics on a recording medium have strong influence on image quality. As one of the indices representing the ink running characteristics of the recording medium, a “spreading rate” is known. It indicates how many times an ink droplet ejected from an ink jet nozzle will spread after arriving on a recording medium, and is given by the following equation:
spreading rate=dot diameter on the recording medium/ink droplet diameter ejected from the nozzle
For example, if an ink droplet of 30 .mu.m diameter during traveling forms a dot of 90 .mu.m diameter on the recording medium, the spreading rate of the recording medium is 3.0. With recording media of small spreading rates, the image intensity is low, and hence, it is difficult to achieve smooth texture, high quality images.
On the other hand, although recording media of a high spreading ratio can increase the image intensity, the following problems arise.
A serial scanning type ink jet recording apparatus as shown in
FIG. 1
sequentially records images of width d as indicated by (1), (2) and (3) in
FIG. 2
by scanning in the direction A the recording head unit
9
including a plurality of ink discharge orifice arrays disposed in parallel. For example, when the number of orifices per array is 256, and the recording density is 400 dots/inch (dpi), the recording width d becomes 16.256 mm (=265.times.25.4/400).
When the volume of ink landing on the recording medium is small, the actual width of the recorded image is approximately equal to the recording width d because the ink is sufficiently absorbed by the recording medium. Accordingly, when recording is performed by repeating the scanning of the recording head unit
9
in the direction A and the subscanning of the head unit
9
by the amount of d in the direction B, joint portions between two adjacent images recorded by two continuous scannings present little problem as shown in FIG.
2
.
The image width, however, may increase to d+.DELTA.d owing to ink running when recording high density portions where the volume of ink is great because the recording medium of a large spreading ratio cannot sufficiently absorb ink. In such a case, the subscanning of the head unit
9
by an amount of d will cause an overlap of images by the amount of .DELTA.d as shown in
FIG. 2B
, thereby resulting in black lines at the overlapped portions. In contrast with this, if the subscanning of the head unit
9
is set as the amount of d+.DELTA.d, white lines will appear at low density portions where the volume of ink is small.
The extra amount .DELTA.d of the image width at high density portions changes depending on the spreading rate of a recording medium, or the volume of ink arriving at the recording medium, and increases consistently with the spreading rate and the ink volume. For this reason, to prevent black lines from occurring, it is necessary to use a recording medium of a small spreading rate, or to reduce the ink volume. In this case, however, the image intensity decreases as stated before, which presents a problem in that smooth texture, high quality images cannot be obtained.
To solve such a problem, the applicants of the present invention proposed the U.S. Ser. No. 679,147. In this proposal, if values of an image signal at the boundaries of the serial scanning exceed a predetermined amount, they are reduced before being applied to recording elements involved in recording the boundaries. This makes it possible to reduce the ink volume discharged from nozzles associated with the recording elements, thereby preventing black lines from occurring at high density, boundary portions.
In this method, the image signal applied to the recording elements associated with the nozzles at the edges of the discharge orifice arrays is converted by a table, the function of which is shown in FIG.
3
: if the input image signal to the table exceeds a predetermined value T, the output of the table fed to the recording elements is restricted at a fixed value F. Thus, in the case where the density of the image signal applied to the recording elements associated with edge nozzles is rather high, the volume of ink discharged from the edge nozzles is restricted, thereby circumventing the occurrence of black lines at the joint portions.
On the other hand, a recording apparatus has been proposed which includes a plurality of recording heads discharging inks of different concentration to improve the gradation of an image. For example, a color image recording apparatus has been proposed which uses several sets of inks, each set consisting of inks belonging to the same color family and having different concentrations, such as light black ink and dark black ink, light cyan ink and dark cyan ink, light magenta ink and dark magenta ink, and light yellow ink and dark yellow ink, thereby improving graininess at highlighted portions. Using this head unit makes it possible to ameliorate the problem in that dots appear unnaturally in highlighted portions in an image recorded by a binary recording type color image recording apparatus.
FIG. 4
shows the schematic arrangement of a conventional color ink jet recording apparatus of this type. This recording apparatus is different from the recording apparatus of
FIG. 1
in the construction of the recording head unit
9
. The recording head unit
9
comprises eight recording heads
9
-
1
BK for light black,
9
-
2
BK for dark black,
9
-
1
C for light cyan,
9
-
2
C for dark cyan,
9
-
1
M for light magenta,
9
-
2
M for dark magenta,
9
-
1
Y for light yellow, and
9
-
2
Y for dark yellow, and four sets of color ink reservoirs, each of which comprises two inks of the same color family with different concentrations. The recording medium
5
is intermittently incremented by the amount of a recording by the recording head unit
9
, and the recording is carried out while the recording medium
5
is stationary. More specifically, the recording head unit
9
is scanned in the direction of the arrow P along the guide rails
6
and
7
discharging ink droplets in accordance with an image signal, thereby forming a color image consisting of dot matrices on the recording medium
5
.
Generally, the signal processing system of
Danzuka Toshimitsu
Fukushima Hisashi
Miura Yasushi
Suzuki Akio
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hallacher Craig A.
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